When it is necessary or desirable to move cargo from one place to another, it is very common to make use of a cargo trailer. A trailer is generally characterized by one or more axles riding on wheels and tires. Heavy-duty trailers tend to have suspension mechanisms similar to those found in cars and trucks, while light-duty trailers often mount the axle or axles directly to the trailer frame. Generally, trailers are designed to be moved using trucks, tractors, four-wheelers, forklifts and similar vehicles. Trailers can also be moved using human effort, but this is generally only suitable for small, light-duty trailers.